ATTITUDE OF WORKING NATURALISTS. 243 



relations of its present flora with that which in earlier 

 ages occupied the arctic zone, might also be referred 

 to. (See preceding article.) 



An excellent instance of the way in which the de- 

 rivative hypothesis is practically applied in these days, 

 by a zoologist, is before us in Prof. Flower's mod- 

 est and admirable paper on the Ungulata, or hoofed 

 animals, and their geological history. We refer to it 

 here, not so much for the conclusions it reaches or 

 suggests, as to commend the clearness and the impar- 

 tiality of the handling, and the sobriety and modera- 

 tion of the deductions. Confining himself " within 

 the region of the known, it is shown that, at least in 

 one group of animals, the facts which we have as yet 

 acquired point to the former existence of various inter- 

 mediate forms, so numerous that they go far to dis- 

 credit the view of the sudden introduction of new 

 species. . . . The modern forms are placed along lines 

 which converge toward a common centre." The gaps 

 between the existing forms of the odd-toed group of 

 ungulates (of which horses, rhinoceroses, and tapirs, 

 are the principal representatives) are mostly bridged 

 over by palaeontology, and somewhat the same may be 

 said of the even-toed group, to which the ruminants 

 and the porcine genus belong. " Moreover, the lines 

 of both groups to a certain extent approximate, but, 

 within the limits of our knowledge, they do not meet. 

 . . . Was the order according to which the introduc- 

 tion of new forms seems to have taken place since the 

 Eocene then entirely changed, or did it continue as far 

 back as the period when these lines would have been 

 gradually fused in a common centre ? " 



